Two-stage centralizer



Sept. 26, 1967 J. R. soLuM 3,343,608.A

Two-STAGE'CENTRALIZER Filed Aug. 10, 1966 wz l M United States Patent O3,343,608 TWO-STAGE CENTRALIZER James R. Solum, Los Angeles, Calif.,assignor to B & W

Incorporated, Torrance, Calif., a corporation of California Filed Aug.10, 1966, Ser. No. 571,604 Claims. (Cl. 166-241) This invention relatesto a device for centering a well pipe in a Well bore commonly known as acentralizer and, in particular, is directed to a centralizer whichproduces a substantially higher centering force after an initial amountof resilient deiiection thereby forming two distinct through continuonsstages of centering capability.

It is relatively common to use centralizer devices for various purposesin the completion of oil wells. One of the primary uses for centralizersis in the cementing of well pipe in the well bore since it is highlydesirable that no portion of the well pipe be in contact with the wellbore which would result in a space devoid of cement. The use ofcentralizers for this purpose is particularly important in well boreswhich are sharply curved or inclined at an angle to the vertical. It iswell recognized that as the curvature or angle of inclination of thewell bore increases the spacing between centralizers must be decreasedor a dilferent type of centralizer producing higher centering forcesmust be used. In some situations both the spacing and the centralizermust be appropriately changed. The most common type of centralizeremploys spring steel bows which resiliently engage the well bore wallbut it is well known that such centralizers will be deected completelyat with no resultant centering in well bores which are extremely curvedor inclined a substantial degree from vertical. As a result, devicesknown as rigid centralizers which employ inflexible ribs that are notsubject to such deiiection are often used in these eXtreme well boreconditions. However these rigid centralizers are also objectionable inmany respects such as being completely inflexible and more likely toadversely affect the well bore wall.

Accordingly it is a principal object of this invention to provide anovel form of well pipe centralizer employing outwardly bowed andresilient staves for engaging the well bore wall in the usual manner andhaving curved straps of a lesser height mounted on the interior of saidstavesl which are urged against the well pipe by the initial resilientdeiiection of the bore-engaging staves and in such pipe-engagingcondition the straps resiliently prevent further substantial deiiectionof the bore-engaging staves thereby providing a second, higher stage ofdeection resisting forces.

It is an object of this invention to provide a two-stage centralizerhaving a plurality of bows extending between collars and abutment strapmeans on the interior of staves to limit resiliently the magnitude ofdeflection of the bows.

Another object of the invention is to provide a novel form ofcentralizer employing a plurality of spring bows functioning both asresilient centering elements and substantially rigid centering elementsin the partially deflected condition.

Other and more detailed objects and advantages of this invention willappear from the following description of the accompanying drawings,wherein:

FIGURE l is a perspective View of the centralizer of this invention.

FIGURE 2 is a sectional plan view of the centralizer of this inventiontaken substantially at the midpoint of the bows.

FIGURE 3 is a fragmentary sectional elevation take through a spring bowsubstantially on the line 3 3 in FIGURE 2 and with the bow in thesubstantially undeected condition.

3,343,6@3 Patented Sept. 26, 1967 FIGURE 4 is a fragmentary sectionalelevation similar to FIGURE 3 but with the bow deected to the conditionfor imposing the second stage high forces in resisting furtherdeflection.

Referring now in greater detail to the drawings, the two-stagecentralizer of this invention is generally designated 10. Thecentralizer 10 is comprised of a pair of collars 11 and 12 and aplurality of bows or staves 13 extending longitudinally between thecollars. The collars 11 and 12 may be of any conventional type or styleand are provided with an inside diameter for tting the well pipe onwhich the centralizer is to be mounted. Although it is not important tothis invention, the collars 11 and 12 may be comprised of two halfcollars hinged together as at 15 for convenience in mounting thecentralizer on the well pipe by permitting the centralizer to be hingedopen and applied laterally to the pipe. As is conventional the collars11 and 12 are axially aligned.

Any number of bowed staves 13 may be employed in the centralizer 10commensurate with accomplishing the desired centering forces andaccording to the size of the device. An arrangement of eight bows isshown in the drawings. The bows or staves 13 are of a preselected prole,as shown in FIGURE 3, and material width and thickness adapted toproduce the desired resilient centering forces when used in a particularwell bore. That is to say, the length of the stave and the magnitude towhich it is bowed outwardly is selected in the usual manner to providethe overall dia-meter at the midpoints of the bows and the resilientcentering forces which are desired in the particular situation. Normallythe diameter formed at the mid-points of the bows 13 will be slightlylarger than the nominal well bore diameter thereby assuring that thewell pipe will be resiliently held in the center of the well bore, atleast in vertical portions of the Well bore. The plural staves 13 arecircumferentially spaced abut the collars 11 and 12 and are securedthereto by any convenient means such as welding 16. As thus fardescribed, the centralizer 10 is substantially conventional.

Means are provided for limiting the amount of free resilient deflectionof each of the bows 13 and, as shown in the drawings, these means may becomprises of a curved strap 14 mounted on the inside of each bow 13.Each of the straps 14 is of a length substantially less than the lengthof the bows 13 and is comprised of at end portions 17 and a bowed orcurved portion 18. The straps 14 are located at the rnidportions of bows13. The end portions 17 make surface contact with the interior side ofthe bow 13 on either longitudinal side of the most outwardly bowedportion of the bowed staves 13 and are secured to the bowed staves 13 byany convenient means such as welding 19. The straps 14 are curved orbowed inwardly a distance substantially less than the amount of outwardbow of the staves 13 as shown in FIGURES 2 and 3. The straps 14 arepreferably of a spring steel for limited resilient deection and are ofsuticient width and thickness to withstand the forces encountered.

Referring more particularly to FIGURES 3 and 4, the centralizer 10 isnormally mounted on a well pipe 9 in any conventional manner such aswith a conventional stop collar 8 or other stop means positioned betweenthe collars 11 and 12 and secured to the well pipe 9. The stop collar 8serves to locate the centralizer 10 on the well pipe and functions topull the centralizer into the well bore 7 by engagement with the lowercollar 12 as the well pipe is lowered into the well bore as shown. Inthe substantially undeflected condition of -bowed staves 13 shown inFIGURE 3 the straps 14 are curved inwardly a distance short of engagingthe well pipe 9. As the lateral forces tending to urge the well pipe 9toward the wall of the bore 7 are increased, such as in an inclined wellbore, the bowed staves 13 on that side of the centralizer will bedeflected producing a resilient resistive centering force. Thedeflection of bowed staves 13 causes some straightening of straps 14 dueto the straightening of the bowed portion of staves 13 between thesecured ends 17 of straps 14. The force required to tend to straightenthe bowed straps 14 of course slightly increases the forces that wouldotherwise be required to deect the staves 13. Continued deection ofstaves 13 ultimately results in the curved portion 18 of the straps 14engaging the exterior of the well pipe 9 as shown in FIGURIE 4 whereuponany further attempted inward deflection of staves 13 subjects the straps14 to compressive bending stresses. Since the ends of straps 14 are xedto the bows 13, any further substantial deilection would requireelongation of that portion of bows 13 or complete collapse of curvedstraps 14. The end result is that the staves 13 are restrained fromfurther inward deection by the straps 14 thereby assuring that the wellpipe 9 will be spaced from the wall of the well bore 7 by the amountshown in FIGURE 4 regardless of the magnitude of the lateral forces.

Thus it may be seen that by this invention there is provided a well pipecentralizer which produces two stages of centering forces with the rststage comparable to the resilient centering forces of conventional bowtype centralizers and the second stage producing forces comparable torigid type centralizers. While the result is two distinct magnitudes ofcentering forces these forces are applied successively withoutinterruption upon continuing `deilection of the centralizer. Althoughthis invention has been described in connection with a particularembodiment it is to be understood that the scope of this invention isnot to be considered as limited to the details herein set forth butrather is of the full scope of the appended claims.

I claim:

1. -In a well pipe centralizer, the combination of: a pair of axiallyspaced and aligned collars adapted to fit the well pipe, a plurality ofcircumferentially spaced and outwardly bowed staves extendinglongitudinally between and mounted on said collars, and a strap meansextending longitudinally of and having ends secured to the interior sideof each stave for engaging the well pipe during inward deection of saidstaves and substantially resisting further inward deflection of saidstaves.

2. The centralizer of claim 1 in which each said strap means is of alength substantially less than the length of said staves.

3. The centralizer of claim 2 in which each said strap most outwardbowed portion of the stave.

` means is centrally located on said stave in relation to the 5 4. Thecentralizer of claim 1 in which each said strap means is curved inwardlybetween its secured ends for resiliently engaging the well pipe.

5. The centralizer of claim 4 in which each said inwardly curved portionof each said strap means is spaced from the well pipe in the undeflectedcondition of the staves for rfirst engaging the well pipe afterpreselected initial inward `dellection of said staves.

6.'The centralizer of claim 1 in which each said strap means is a shortcurved bow of spring steel located at the most outwardly bowed portionof said stave and bowed inwardly short of engaging the well pipe in theundeected condition of said stave, and said strap means having a radiusof curvature substantially less than that of the portion of the stave towhich the strap means is attached.

7. The centralizer of claim 6 in which each said strap means has a atend portion engaging the interior of the stave in surface contact.

8. The centralizer of claim 7 in which said end portions are welded onlyat their extreme ends to the stave.

9. In a well pipe centralizer of the type having a pair of axiallyspaced and aligned collars adapted to lit the Y well pipe and aplurality of circumferentially spaced and outwardly bowed stavesextending longitudinally between and mounted on said collars, theimprovement comprising: a strap means extending longitudinally of andhaving ends secured to the interior of each stave for imposing only aslight resistance to the initial inward deection of said staves, saidstrap means engaging well pipe to impose a substantial resistance tofurther inward dellection of said staves beyond said initial amount.

10. The centralizer of claim 9 in which each said strap means is a shortcurved bow of spring steel located at the most outwardly bowed portionof said stave and bowed inwardly short of engaging the well pipe in theundeflected condition of said stave, and said strap means having aradius of curvature substantially less than that of the portion of thestave to which the strap means is attached.

References Cited UNITED STATES PATENTS 1,412,213 4/1922 Mowers 166-202 X1,835,377 12/ 1931 Clark e al 166-241 X 2,368,737 2/ 1945 zBadgley166--241 X 2,656,890 10/ 1953 Brandon 166-241 3,312,285 4/ 1967 Solum166-241 CHARLES E. -OCONNELL, Primary Examiner.

DAVID H. BROWN, Examiner.

1. IN A WELL PIPE CENTRALIZER, THE COMBINATION OF: A PAIR OF AXIALLYSPACED AND ALIGNED COLLARS ADAPTED TO FIT THE WELL PIPE, A PLURALITY OFCIRCUMFERENTIALLY SPACED AND OUTWARDLY BOWED STAVES EXTENDINGLONGITUDINALLY BETWEEN AND MOUNTED ON SAID COLLARS, AND A STRAP MEANSEXTENDING LONGITUDINALLY OF AND HAVING ENDS SECURED TO THE INTERIOR SIDEOF EACH STAVE FOR ENGAGING THE WELL PIPE DURING INWARD DEFLECTION OFSAID STAVES AND SUBSTANTIALLY RESISTING FURTHER INWARD DEFLECTION OFSAID STAVES.